The basic requirements for polymeric materials in some areas of medical application are that they be hydrophilic, soft and oxygen-permeable. The prior art teaches the use of many different polymeric materials in medical areas such as in contact lenses, in artificial membranes e.g., artificial skin for surgical and burn dressings, membranes for an artificial lung machine, in other prosthetic devices such as prosthetic eye, pacemaker and other devices such as intrauterine, etc. Although these polymers possess certain desirable properties for their specific medical application, they suffer from other undesirable characteristics which reduce their utility.
In contact lens area, the hard lens material, polymethylmethacrylate (PMMA), is rigid and durable but relatively impermeable to oxygen and further suffers from being hydrophobic. The hydrogel contact lens based on hydrophilic polymers such as polyhydroxyethyl methacrylate (Poly HEMA) are soft but with poor durability and dimensional stability. It also does not have enough oxygen permeability.
The copolymers taught in U.S. Pat. No. 3,808,178 for contact lens fabrication are with relatively high oxygen permeability, but suffer from being rigid and relatively hydrophobic.
Another polymeric material is silicone rubber such as polysiloxane which is most widely used in a medical application, such as in a prosthetic eye, pacemakers, heart valves and intestinal sections. It is also used in contact lenses and artificial lung machines, etc. Although it is soft, resilient and is highly gas permeable, it is hydrophobic. Due to the low strength of polysiloxane, a filler which increases the refractive index of the mixture, must be added to improve the durability.
Accordingly, it would be highly useful in a number of medical applications to provide a polymeric material having increased hydrophilicity, softness after hydration, and oxygen permeability. For contact lenses, this material provides a combination of properties that are close to an ideal combination of properties of the best features of the hard lens material, PMMA, soft lens material, poly HEMA, silicone rubber and the Gaylord copolymer lenses. For other prosthetic devices, features such as increased hydrophilicity, softness after hydration and gas permeability are also very useful and desirable. The inventive composition has been found to provide the above features.